Hello I am new here and this is my first post so I do thank you for the opportunity.
I have an old NAD 7240PE that smoked and blew a capacitor when plugged in. This happened several years ago and I shelved the NAD since then. Recently I took it out to visually inspect the PCB and I am using it as a platform to learn electronic components etc. So a bit of an odd ball project. Don't worry though, I love this little amp and will do everything I can to revive it. It has a special place in my heart.
As I was busy removing all the old electrolytic capacitors I also spent several hours reflowing almost every solder joint on the amp side PCB (there are two PCBs in this NAD). I followed up with cleaning the flux off the board with using 99.9% isopropyl alcohol and a brush. To my dismay I discovered that a shiny coating applied over the PCB washed off with the flux. The said PCB now has a rather dull flat looking finish as compared to the other remaining PCB that has been barely touched. I don't know what the name of the coating or finish on the PCB is and whether it is a deliberate process to maintain or protect the PCB or if it is a left over residue from what might have been wave soldering.
The coating, as I call it, leaves the board with a shiny non-tacky finish and makes the green color of the PCB really have a nice punchy color to it. I would like to restore the said PCB with an equivalent material. The remaining PCB does have this shiny surface, as mentioned, still in place and its appearance seems to suggest that it may have applied manually with some sort of a brush or maybe sprayed but it is a bit clumpy to suggest that latter. Does this coating/process have a proper name and can I still buy this material so that the board can be returned to an out of the box finish?
I am leaving a few images of the PCBs as a reference.
This first image illustrates what I call a coating. You can see that the lower board has a much shinier finish. On touch, it is non-tacky. It also comes off very easily with isopropyl alcohol.
This next image is a the glossy finish coating from another angle.
I have an old NAD 7240PE that smoked and blew a capacitor when plugged in. This happened several years ago and I shelved the NAD since then. Recently I took it out to visually inspect the PCB and I am using it as a platform to learn electronic components etc. So a bit of an odd ball project. Don't worry though, I love this little amp and will do everything I can to revive it. It has a special place in my heart.
As I was busy removing all the old electrolytic capacitors I also spent several hours reflowing almost every solder joint on the amp side PCB (there are two PCBs in this NAD). I followed up with cleaning the flux off the board with using 99.9% isopropyl alcohol and a brush. To my dismay I discovered that a shiny coating applied over the PCB washed off with the flux. The said PCB now has a rather dull flat looking finish as compared to the other remaining PCB that has been barely touched. I don't know what the name of the coating or finish on the PCB is and whether it is a deliberate process to maintain or protect the PCB or if it is a left over residue from what might have been wave soldering.
The coating, as I call it, leaves the board with a shiny non-tacky finish and makes the green color of the PCB really have a nice punchy color to it. I would like to restore the said PCB with an equivalent material. The remaining PCB does have this shiny surface, as mentioned, still in place and its appearance seems to suggest that it may have applied manually with some sort of a brush or maybe sprayed but it is a bit clumpy to suggest that latter. Does this coating/process have a proper name and can I still buy this material so that the board can be returned to an out of the box finish?
I am leaving a few images of the PCBs as a reference.
This first image illustrates what I call a coating. You can see that the lower board has a much shinier finish. On touch, it is non-tacky. It also comes off very easily with isopropyl alcohol.
This next image is a the glossy finish coating from another angle.
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Conformal coating is what it is called. Used to protect the copper tracks.
Otherwise known as PCB Varnish; https://uk.rs-online.com/web/p/electronics-varnishes/1181554
Otherwise known as PCB Varnish; https://uk.rs-online.com/web/p/electronics-varnishes/1181554
Thank you everyone. I am grateful for the replies and the product link. I will study this further. Much appreciated! 🙂👍
By the way, this looks like an excellent forum! Cheers!
By the way, this looks like an excellent forum! Cheers!
One question on conformal coatings. I imagine this may impede making simple measurements such as a continuity test. Do these products come in a small bottle with a brush as well? I know I can google this but I prefer to ask the experts here. Thanks again!
It will. Sharp probes will usually break through. I haven’t seen too many consumer products with conformal coating on their PCB.
It’s probably acrylic based and acrylic can be upset by isopropyl alcohol. Acrylic is the most common stuff. MG Chemicals make spray on products available at Digi-Key.
Good luck.
It’s probably acrylic based and acrylic can be upset by isopropyl alcohol. Acrylic is the most common stuff. MG Chemicals make spray on products available at Digi-Key.
Good luck.
I used to do model cars. The small-job trick is to spray a little into the can lid, and then pick some up with a brush to get into small areas.
Yes, if you were doing hundreds you would want jar-paint, but for a small area it is not worth having another product. (And some of the odd colors we used on 1960s model cars were not available bulk.)
I tend to spray the conformal coating into a little container and then pour and brush it on. It covers really easily. Use a child's small soft paint brush and you can cover large areas in no time. As it dries very quickly you can find the solvent evaporation is so quick that the board actually cools and can easily get condensation on it if done in a cold setting. Just something to be aware of.
The board will look better than new once you coat it 🙂
The board will look better than new once you coat it 🙂
By the way; what do you mean by phenolic? Your boards are fiberglass/epoxy commonly referred to as FR-4 but there are tons of variations (multifunctional/tetrafunctional ) and on and on. Phenolic resins haven’t been used for quite a while.
Conformal coating my butt. That just looks like a layer of residual rosin flux from the wave soldering process. It's pretty common for them to leave it. You cleaned off the flux, both yours and theirs and the board is better off for it. Boards do get conformal coated, but it's rare in consumer equipment. Really rare. There are many pitfalls to doing it because you can seal in things you don't want. The board needs to be really clean and dry. Easiest thing for you to use is common Krylon clear plastic spray. They used to sell it as an electronic coating with a different label but I don't see it around. Wish I had saved my can just to take a photo. AFAIK, it was exactly the same stuff as the common clear plastic spray. The Krylon is nice because you can solder through it. Some of the "real" coatings are extremely tough and make repairs more difficult. This is the classic stuff- https://chasecorp.com/HumiSeal/
That’s an old piece of kit like from the 90’s I think. Pretty big reliability (read warranty ) deficit to leave a flux on the PCB after manufacturing if it’s not no clean. You could be right but I have never seen flux be glossy.
By the way; Humiseal covers silicone, epoxy, polyurethane and acrylic plus some hybrid chemistries. A pretty broad range. I have a lot of experience with 1B31 (acrylic) and IIRC 2A3 which is polyurethane. Back before Chase bought Humiseal.
One simple way to be sure, would be to treat it just like flux and lightly press the hot soldering iron tip on an unused part of the coated copper foil laminate. If the coating melts and flows without scorched residue, it's most likely flux. If its an acrylic or similar varnish-come-conformal coating, it'll fry and carbonise right where is, like any paint.
Well, it looks just like many receivers I've seen. Some Dynaco boards were also like that. Rosin flux is pretty inert and doesn't usually cause any problems if left in place. I wouldn't want it on high impedance circuitry, but an awful lot of equipment was built with no cleaning. It's the modern fluxes that are a disaster if not cleaned right away.
I used Phenolic because I was informed, perhaps incorrectly, that the PCB is of this material. Sorry if this added some confusion.
Given the age it is possible it's phenolic. I still have some late 1980s through early 2000s tape recorders and most of the boards in those machines are phenolic.
I am not sure what you mean by the "unused part of the coated copper foil laminate", that being said I can share this with you and the rest of the audience. When reflowing the solder, I found little to no need for using flux. I otherwise use flux as it really helps the solder to flow and shape very nicely. As a reminder, I literally went throughout the entire PCB while wearing a headband magnifying glass.
To answer your question as it were, I can assure you that the following observations were made starting this thread:
- Firstly, the shiny finish is not tacky at all. It feels very smooth while running my finger tips over it.
- Before posting here I was personally under the impression that this finish, or coating was flux because its scent was not unlike flux. It appeared to lend itseld to reflowing the solder.
- After reflowing all the solder joints, I cleaned the entire board with an old soft toothbrush dipped in isopropyl alcohol. This is something I generally do anyway when it comes to vintage Macs. I was disappointed to learn that spot cleaning with iso left those areas of the board looking unlike the rest of the PCB. Preferring a uniform appearance I chose to clean the entire PCB.
- While brushing the PCB I could see that the material was very soluble. It should also be noted that as I brushed in a circular motion all around the board, the material took on a slightly opaque milky (white) appearance — this was very subtle though.
- From time to time I would use a sheet of paper towel to clean/dry the brush and the brush left a light brown/golden stain on the paper towel.
- I actually believed I was removing flux from the PCB because it reminded me of the process.
- After having cleaned the board as best as I could and leaving it to dry, I began to think that I cleaned off flux so I thought I should hand paint some liquid no clean flux on the board to return it as I found it but it never took on the same shine as originally found and it remained tacky. Maybe it has to cure for a while? As I write this, I wonder if a blow dryer might be able to trigger a shinier finish to the flux I hand painted.
It could be that this shiny finish (coating as I called it) is simply flux after all — something left behind from the manufacturing process. As per your specific point that I quoted at the top, I reread it and in fact I was able to slide the tip of my iron along a rather hefty trace and the original solder just flowed without any effort. For some reason a liberal amount of solder is to be found on these large traces.
I know it was a long reply but I tried to be as thorough, as descriptive and as detailed about my humble steps as I could so that a clear conclusion can be drawn. I do consider myself as still learning — electronics is a hobby that I really love and as I gather more knowledge and seek answers I do appreciate each and everyone of your answers very much indeed. I do hope this helps.
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Given the pcb will be inside a case I would just leave it.
Starting to spray or brush on coating might get on solder contacts and insulate them from measurements or even make soldering difficult.
Starting to spray or brush on coating might get on solder contacts and insulate them from measurements or even make soldering difficult.